Let me start by saying that I do not own either phone. I'm actually still rocking a Galaxy SII (rooting running JB)...
SGSIII and IP5 are both awesome phones in terms of hardware, and both are running awesome software, though very different...
My biggest problem with Apple (for me, a relatively tech savvy person) is how they limit what you can do. Be it not being able to change a hard drive on certain macbooks without first taking it in to an apple store, being forced to use Itunes to sync with my phone, and having to use proprietary cables/accessories.
I get that some people want a device that works, and nothing more. I get that some people don't have time to mess with,customize, or personalize a device, and will pay a premium for hardware that might not really be the best available (not bad by any means, but good luck upgrading the specs on any apple device).
To put it simply, on principle, I'd keep my GSII and my freedom, up against pretty much anything apple puts out, regardless how great the hardware is.
I wouldn't buy a car, if I couldn't change the brand of tire, use different oil, add an intake if I want (not saying I would, just want to be able to).... SOOOOOO... Why would I buy a phone from a company that decides everything for me...
Btw this isn't neccessarily pro-Android, but pro- do what I want with what I buy... which Android lets me do the most of... for now anyway